Creatine Kinase–MB: The Journey to Obsolescence

Gurmukh Singh, MD, PhD, MBA; Paramdeep S. Baweja, MD

Disclosures

Am J Clin Pathol. 2014;141(3):415-419. 

In This Article

Abstract and Introduction

Abstract

Objectives. To evaluate the clinical utility of and demand for the creatine kinase (CK)–MB assay.

Methods. We examined the number of CK-MB tests from 2007 through 2013 while we progressively deemphasized their use. We first removed CK-MB from the acute coronary syndrome (ACS) panel and then from the main menu and observed the demand for the test. We also reviewed patient medical records to assess the appropriateness of its use.

Results. After removing CK-MB from the ACS panel, the test volume dropped from around 12,000 per year to about 150 per year. In reviewing the records of 171 patients who had CK-MB determination done over a 28-month period, we discovered that CK-MB contributed to the diagnosis in only one patient, although it was not essential. Since removing CK-MB from the laboratory menu, two CK-MB tests were ordered in 4 months, and neither added value.

Conclusions. CK-MB determinations do not add value to information available from the troponin assay and can be safely removed from the laboratory menu.

Introduction

Laboratory tests for the diagnosis of myocardial injury in general, and myocardial infarction (MI)/acute coronary syndrome (ACS) in particular, have been and still are in the process of evolving. Serum aspartate aminotransferase (AST), creatine kinase (CK), and lactic dehydrogenase, including isotypes of the latter, were used for diagnosis and served the purpose when no active interventions were taken for the treatment of ACS.[1] Serum assay for myoglobin provides an early indication of ACS but has a large number of false positives and is not in common use.[2] Introduction of the CK-MB assay provided a major advance in the early diagnosis of MI or ruling out MI. The test is a two-step process requiring determination of total CK and measurement of the MB fraction. An assay for the MB fraction has progressed to an immunoassay and does not require physical subfractionation of CK.[3]

Introduction of assays for troponins T and I has allowed slightly earlier diagnosis of ACS and improved the sensitivity over CK-MB. Some laboratories have stopped offering CK-MB in the workup of ACS.[4,5] The search for better markers and panels of markers for myocardial injury is continuing.[6–8]

Just as there is a lag in introducing new tests and treatments even after the utility of the same has been demonstrated, there is a lag in discontinuing outdated tests and treatments. For example, bleeding time and erythrocyte sedimentation rate continue to be offered and used in some institutions. Experts have recommended discontinuing CK-MB testing for the diagnosis of MI.[4,9] It appears that testing for CK-MB has reached obsolescence, and we present our experience in the journey of the change in CK-MB testing.

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